I started out with Heresy's/Zen C, a nice combination. Keep in mind you'll need a phono stage of course to run into your ZSLA-1 if you want to listen to vinyl. The ZSLA should be much like running direct into the Zen, in terms of gain it won't add any so you'll need to make sure you have a CD player with healthy output (>2V) to make sure you can get full output.

Heresy's should give you good headroom, they won't shake the walls with a Zen but to a large extent that's missing the point (of going this route) anyway.

It's true the input sensitivity of the se84 zen is high enough to go without a pre for many line level sources. I listened to my se84cs straight from a cd source w/o a pre for a year. The transparence and quickness was pretty amazing, but musicality is SO much better with a pre, imho.

I run a ZSLA-1 Sig. into the front inputs on my SE84CSEX. I don't believe that the C has the front inputs. You might consider sending it to Steve ( or doing it yourself, it's fairly simple ), to have them put in. Bypassing the existing pot and wiring would do nothing but good things to the sound of the combo. The ZSLA-1 Sig. is the most revealing preamp I've ever heard, and I've heard some very good ones.